The invention relates to a device for supplying cooling air under pressure, e.g. for cooling the electric apparatus in an aeroplane at rest on the ground, comprising an internal combustion motor, such as a diesel motor; an air compressor having its suction line connected to the atmosphere, the pressure side of this air compressor supplying air under pressure; a cooling circuit for cooling this air under pressure, said cooling circuit including a compressor, a condenser and a cooler.
In a known device for cooling the electric apparatus of an aeroplane which is at rest on the ground outside air is compressed by means of an air compressor, whereafter this air under pressure functions as the cooling air. However, the air is increased in temperature in the air compressor, which increase amounts e.g. to approximately 30.degree. C. As the cooling air should have a temperature which is e.g. below 26.degree. C. for the object in view, the air under pressure supplied by the air compressor has to be cooled unless the temperature of the outside air is very low, viz. lower than -4.degree. C. in case of an increase of the temperature in the air compressor of approximately 30.degree. C. Generally, freon is used as the circulating medium in the cooling circuit.
This known device has the disadvantage that the cooler of the cooling circuit has to have a very large capacity and consumes much energy, the more so as this cooler has to be switched on practically continuously. As large differences in the temperature of the outside air occur a complicated control apparatus is required, which again consumes much energy.